Assessing the impact of anthropogenic activities on phytoplankton diversity in Ntinda stream.
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Ntinda stream is located in Ntinda, one of the areas in the capital city of Uganda (Kampala) zoned for industrial development and include industries which discharge effluents into the stream without adequate treatment. This greatly impacts on the biotic community of the stream which includes planktons as the major component of food web structure in aquatic ecosystems and whose distribution and community structure are driven by the combination and interactions between physical, chemical, and biological factors within the environment. In the present study, water quality and the community structure of phytoplankton were investigated weekly from January 4th to January 30th 2020 at 3 sampling sites along the gradient course of Ntinda stream. Results from the study indicated nutrient pollution with the highest value of phosphorus concentration in site3 (0.52 ± 0.05) and the lowest value in site1 (0.062 ± 0. 01*), total nitrogen concentration as highest in site2 (3.13 ± 0.117) and lowest in site1 (0.24 ± 0.039*), TDS as highest is site2 (2 53.8 5 ± 44.12) and lowest in site 3 (14 6. 85 ± 6.87), EC as highest in site2 (377.45 ± 19.42*) and lowest in site1(295.65 ± 11.37), pH as highest in site2 (8.07 ± 0.14*) and lowest in site1 (7.39 ± 0.19), DO as highest in site1(7.575 ± 0.31) and lowest in site2 (4.45 ± 0.34) while temperature had the highest value in site2( 24.3 ± 1.19) and the lowest value in site 3 (21.725 ± 0.86). There was a significant difference for each of the water parameters in the three sampling sites marked by the asterisk. Microscopic analysis showed that phytoplankton comprised 53 species belonging to seven classes in which Cyanophyceae, Chlorophyceae and Bacillariophyceae accounted for the most important constituents of the river’s phytoplankton assemblage. Microcystis sp. and Spyrogyra hyalotheca existed in all the three sites where Microcystis sp. was most abundant in site3 while Spyrogyra hyalotheca was most abundant in site2. High value of Shannon-Wiener's index (H ') was recorded in Site1 (0.71), followed by Site3 (0.68), and then Site2 (0.64). It means that diversity index of Site1 and Site3 of the stream are categorized as moderate stable community, while Site2 is categorized as unstable community. The Simpson (dominance) index varied from 0.64 to 0.70 and the highest value was in Site3 (0.70) followed by Site1 (0.65), and Site2 (0.64). The index ranges from 0-1, meaning there is a high dominance since the value was greater than 0.5.A correlation analysis between phytoplankton diversity and water parameters exhibited negative correlation for all water parameters in all the sampling sites except for Dissolved oxygen which exhibited a positive correlation this implied that high temperature in the water depleted the oxygen leading to the increase in genera diversity. Basing on the results of water parameters and phytoplankton abundance and diversity, Ntinda stream is under rising pollution pressure and constant monitoring by the relevant authorities and proper management of the stream is required.